Magnetic-field-induced chain-like assembly structures of Fe ₃ O ₄ nanoparticles

Abstract

By controlling the time to apply magnetic field to a Fe3O4 magnetic fluid with polymer acrylic resin and by evaporating the solvent, linear chain-like structures were obtained and fixed. Optical microscopy and transmission electronic microscopy (TEM) were used to observe the assembly structures of the fixed magnetic nanoparticles. We found that the chainlike structures with size even down to hundreds nanometers had smaller substructures. A picture of aggregation between linear chain-like substructures is proposed to understand the formation of the macrostructure in magnetic fluid induced by a magnetic field. Two basic aggregations, the coarsening and the connection of the substructures, were observed.

Direct observations of field-induced assemblies in magnetite ferrofluids

“…2,3,11,[36][37][38][39]45,48 There are many factors that influence the morphologies of field-induced microstructures such as dipolar strength, magnetic field orientation and strength, thickness of the sample, polydispersity, concentration of the particles, and temperature. In a qualitative view, the morphology of the structures depends on particle-particle interactions characterized by k, as well as particle-field interactions characterized by a where a ¼ mH/k B T, known as energy ratio or Langevin parameter and H is magnetic field strength.…”

“…1,[36][37][38][39][40] A variety of experimental techniques has been used in order to observe formation of structures. Amongst these techniques are SEM (Scanning Electron Microscopy), TEM (Transmission Electron Microscopy) and Cryo-TEM (Cryogenic Electron Microscopy), Optical Microscopy, small-angle neutron scattering (SANS), 41 light scattering and scattering dichroism, Raman spectroscopy, 42 and X-ray scattering (SAXS), 2,3,27,[45][46][47] each with its advantages and disadvantages. For instance, it is argued that TEM method may not give an accurate feature of the evolution of dipolar structures in liquid phase because during evaporation of the solvent distortions and sometimes cracks are formed by surface tension.…”

Magnetic Nanoparticles Aggregation in Magnetic Gel Studied by Electron Magnetic Resonance (EMR)

“…However, it has a poor sensitivity with fields with a strength higher than 1,000 G. Thus in [5] the parameter of magnetic anisotropy obtained by the torque angle technique changes slightly (15%) for the magnetic gels formed in the field range 1,000-10,000 G. The torque angle technique gives quantitative information on the magnetic anisotropy of samples but it does not allow the quantitative estimation of the aggregates aspect ratio. Transmission electron microscopy (TEM) and scanning electron microscopy (SEM) can also be applied to research particle ordering [5][6][7][8]. However, this method requires special preparation of samples and does not give unambiguous results for magnetic gels [5].…”

Strong Magnetic Field Induced Segregation and Self-Assembly of Micrometer Sized Non-Magnetic Particles

“…According to the literatures [27,28], the lateral aggregation or coarsening can only be evoked in a rather high particle concentration due to collision or energy decline. The aggregation is usually observed at the end of the chains since the potential energy for the particle located near the end of a chain is much lower [3,5].…”